Virial mass, M_vir, of the 164 GMCs as a function of luminosity, L_CO, from the current survey (filled circles). The line present a best fit to the data with slope of ﹩1.1\pm 0.1﹩. Open circles are for the clouds from the first survey (Fukui et al. 1999; Mizuno et al. 2001b). The virial masses of clouds from the first survey were recalculated after subtracting the NANTEN beam size from the sizes of the clouds shown in the catalog of Mizuno et al. (2001b).